From Spore to Harvest: Navigating the Mushroom Growth Cycle

A mushroom’s spores contain the blueprint for future growth. Spores are released from a mature mushroom and can be dispersed via air, water or hitching a ride on animals.

Cultivators use spores to colonize grain-based substrate, which is then known as a “spawn cake”. A drop in temperature and increased fresh air exchange can stimulate the mycelium into creating knots or primordia that will develop into mushroom fruiting bodies, likewise a 95°F-120°F is ideal for drying mushrooms.

Colonization

Cultivators of mushrooms work to create the right conditions for colonization by encouraging mycelium growth through careful preparation of substrate. This includes ensuring moisture content is optimal, making sure the material is free of contaminants, mixing if needed and adding supplemental nutrients to encourage rapid growth. Often, cultivators will use a mixture of materials such as logs, stumps, straw, coffee grounds, grain hulls and sawdust as the substrate. The process of preparing the substrate will be guided by the type of mushroom being grown and the equipment available for culturing.

In the wild, mushrooms grow as part of a symbiotic relationship with trees through a process called mycorrhiza. This is a mutually beneficial relationship whereby the mushroom provides trees with water and minerals that they cannot extract from the soil. In turn, the trees provide mushrooms with sugar compounds and other organic matter that they cannot produce by themselves.

While this is a wonderful benefit for the ecosystem, it means that fungi are not as easily accessible for human consumption. Mushrooms also lack chlorophyll so they are unable to take up food from the air and must instead obtain their nutrients through substrate. This is why most mushrooms are found growing in the ground or under the bark of a tree rather than floating in a puddle in the forest floor.

When a fungus is ready to reproduce, it sheds millions of microscopic spores that are similar in appearance to seeds. These spores are spread by wind, rain or insects and eventually land in new environments where the conditions are right for fungi to colonize.

The spores of some fungi are shaped like an umbrella and feature thin, bladelike gills on the underside of the cap. Others, such as members of the order Boletales, feature pores that open in a layer on the underside of the cap. The shape of the spores helps to differentiate between different species of mushroom.

When examining the underside of a mushroom cap, note not only what the gills or pores look like but what color they are. This can help to determine the genus and species of the mushroom, as well as if it is safe to eat.

Primordia

As mushrooms grow they move through several stages of development. A deep understanding of these stages and the environmental triggers that affect them is essential for a successful mushroom cultivation process. From spore germination through to the formation of mature fruiting bodies, each stage is crucial to the success of a crop.

Spores are released by a mature mushroom as a way to reproduce, landing on a suitable substrate and beginning the colonization process. After a period of time, the mycelium begins to expand at a rapid rate and looks for water and nutrients. When a fungus is growing in the correct habitat, mycelium will meet up with a similar mycelium and begin to combine, forming long, thin threadlike strands known as hyphae. Over time, the repeated combining of hyphae creates a large network called mycelium. Mycelium is the foundation for all mushrooms and acts as their roots, allowing them to absorb nutrients and fight off any environmental threats that may stunt growth.

The mycelium can be found on any material that contains cellulose, including wood and straw. Mushrooms form on a porous, permeable substrate such as casing soil or a mixture of peat and ground limestone. Casing soil is often referred to as “mushroom compost” because it is a great place to start for new fruiting mushrooms. The casing soil serves as a water reservoir and a place for rhizomorphs to develop, which are the earliest forms of mushroom roots. The rhizomorphs connect the mycelium to the rest of the world and provide a food source for the fungus.

Once the mycelium has reached sufficient size, it will begin to form a dense cluster of mycelial growth on top of the casing soil, called a hyphal knot. As a result of mycelium growth, the hyphal knots will begin to take on the shape of mushrooms. During this time, the development of mushrooms is extremely sensitive to environmental conditions. Temperature changes, nutrient availability and light exposure can all cause the primordia to abort.

Over the course of a few days, the hyphal knots will begin pinning out, meaning that they are starting to develop gills and a cap. The duration of the pinning stage varies by species and environmental conditions, but generally lasts for between five and 12 days. This is also a critical time for maintaining optimal environmental conditions.

Fruiting

Like plant seeds, mushroom spores germinate (sprout) under the right environmental conditions. These include high humidity and a favourable temperature for that species of mushroom. Once germination occurs, the mycelium spreads throughout the substrate to gather water and nutrients. As it does, it forms knots, or primordia, that develop into young mushrooms over a period of days. The process of producing these knots or primordia is known as fruiting.

Cultivators manipulate the environment to stimulate fruiting and ensure that mushrooms develop at a consistent rate. They do this by controlling the temperature, introducing fresh air, and adjusting the moisture content of the substrate. The timing of this process depends on the season and species, with most edible mushrooms fruiting in summer and fall, though some, like Morels, can be found year-round.

Indoors, growers use a variety of set-ups depending on their preferred method. Closets and basements can be a good choice because they’re dark and warm, and some mushroom cultivators use specialized containers like monotubs or martha tents to dial in the optimum environmental conditions for a given crop.

Spores drop from the cap when the conditions are right for that particular species, so if you’re collecting mushrooms in nature, place the mushroom with its gills facing down on a sheet of paper or aluminum foil, or an index card, and wait a few hours for it to release its spores. You can then examine the spore print, which appears as patterns on the surface of the paper or foil.

Once the spores are released, they’ll be carried away in the wind and drop into other favourable environments for that specific species. For example, the spores of Morels will be drawn to forests where they’ll find the conditions they need to sprout and mature. As they do, the Morels will break down, releasing even more spores and beginning the cycle anew. This is one of the many ways that mushrooms can help sustain a healthy ecosystem. In fact, fungi like Morels are so beneficial to the ecosystem that the USDA lists them as an endangered species in the wild.

Harvesting

Fungi have a unique way of reproducing. Most mushrooms release spores – little seed-like structures that contain the code for life (DNA) and a cellular machine that will grow into another mushroom when conditions are right. Spores disperse into the air and float around until they land in a favorable environment where they will germinate and become a new individual fungus. Depending on the type of mushroom, this process may be asexual or sexual, or a combination. Many fungi have specialized spore-releasing structures like gills, gametangia and sporophores.

Mushrooms start their lives as white flufff called mycelium. In the wild, mycelium can live underground for a long time. But if the conditions are right, mycelium can send out tiny buds that will seek out daylight. When the buds reach the surface, they form a mushroom cap – the “flower or fruit” of the fungus that disperses its spores.

The gills on the underside of the mushroom are lined with tiny holes, or pores, that give the mushroom its distinctive color and shape. Each pore contains tens of thousands of microscopic spores – so small that it takes 25,000 of them to cover the tip of a pinhead! A single gill can produce billions of spores over the course of a day.

If the gills have a yellow or red tint, it indicates that the fungus is ready for harvesting. A mushroom’s flavor and quality deteriorate rapidly after it is harvested, so it must be picked just before the gills begin to darken. Mushroom farmers call this time of transition a flush, break or bloom.

During this phase, mushrooms can be stored for several weeks at room temperature or refrigerated. The key is to keep the compost at the proper temperature and humidity so that the spawn continues its growth. Adding nutrients to the compost at this stage is called supplementation and can improve the yield of the crop.

During the harvesting process, workers remove a portion of the compost that contains the mushroom rhizomorphs. This step is critical in ensuring that the next flush of mushrooms will continue growing to maturity. This is also the time when contamination by weed molds, nematodes and pathogens should be controlled to prevent spoilage.